Hybrid vehicle

ABSTRACT

A vehicle includes an engine, an MG (motor generator) 1, an MG2, a planetary gear device mechanically coupled to the engine and MG1 and MG2, a battery, a converter configured to boost a voltage from the battery, an inverter configured to perform a power conversion between the converter and MG1 or between the converter and MG2, and a controller. MG1 generates a counter-electromotive voltage when rotated by the engine, and a braking torque is generated as the counter-electromotive voltage becomes greater than the output voltage of the converter. During an inverter-less running control where the inverter is put into a gate shut-off state and the engine is driven to cause MG1 to generate the counter-electromotive torque, the controller decreases a voltage difference between the counter-electromotive voltage and the output voltage of the converter when a chargeable power of the battery is lower than a predetermined value.

This non-provisional application is based on Japanese Patent ApplicationNo. 2015-179706 filed on Sep. 11, 2015 with the Japan Patent Office, theentire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a hybrid vehicle capable of running byusing at least one of the motive power from an engine and the motivepower from a rotating electrical machine.

Description of the Background Art

Japanese Patent Laying-Open No. 2013-203116 discloses a hybrid vehiclewhich is provided with an engine, a first rotating electrical machineincluding a rotor provided with a permanent magnet, a second rotatingelectrical machine, a planetary gear mechanism, a battery, a converterconfigured to boost a voltage from the battery, and an inverterconfigured to perform a power conversion between the converter and thefirst rotating electrical machine and between the converter and thesecond rotating electrical machine. The planetary gear mechanismincludes a sun gear coupled to the first rotating electrical machine, aring gear coupled to the second rotating electrical machine, and acarrier coupled to the engine. In this hybrid vehicle, if there occurs amalfunction such as the first rotating electrical machine and the secondrotating electrical machine cannot be electrically driven by theinverter normally (hereinafter referred to as “inverter malfunction”), acontrol will be performed so that the inverter is brought into a gateshut-off state and the engine is controlled to drive the vehicle to rununder a fail-safe mode.

SUMMARY OF THE INVENTION

As described in Japanese Patent Laying-Open No. 2013-203116, when amalfunction occurs, the inverter is brought into a gate shut-off stateand the engine is controlled to drive the vehicle to run under afail-safe mode, this kind of control will be referred to as“inverter-less running control” in the present specification.

In the inverter-less running control, while the inverter is beingbrought into the gate shut-off state, the first rotating electricalmachine is dynamically (mechanically) rotated by the rotational forcefrom the engine, and thereby generating a braking torque. In otherwords, as the first rotating electrical machine is rotated by therotational force from the engine, it generates a counter-electromotivevoltage. The counter-electromotive voltage will take a higher value asthe rotation speed of the first rotating electrical machine is higher.As the counter-electromotive voltage exceeds an output voltage from theconverter, a current is generated in response to a difference betweenthe counter-electromotive voltage and the output voltage of theconverter (hereinafter simply referred to as “voltage difference”),flowing from the first rotating electrical machine to the battery. Inother words, the first rotary electrical machine generates acounter-electromotive power in response to the voltage difference, andcharges the battery with the counter-electromotive power. In response tothe counter-electromotive power, a torque (hereinafter referred to as“counter-electromotive torque”) is generated in the first rotatingelectrical machine. The counter-electromotive torque is a braking torqueacting in a direction to prevent the first rotating electrical machinefrom rotating. Due to the action of the braking torque(counter-electromotive torque) from the first rotating electricalmachine on the sun gear, a drive torque is generated in the ring gearacting in a positive direction as a reaction force against the brakingtorque (counter-electromotive torque) from the first rotating electricalmachine. Owing to the drive torque, the ail-safe mode is achieved.

However, it is concerned that during the inverter-less running controlthe following problems may arise. Specifically, in the inverter-lessrunning control, the battery is charged by using thecounter-electromotive power generated by the first rotating electricalmachine, an SOC (State Of Charge) indicating a charged amount of thebattery will rise. Generally, when the SOC is in a highly chargedregion, in order to prevent overcharging, the chargeable power (inwatts) of the battery is narrowed down to a smaller value as the SOCincreases. Therefore, when the inverter-less running control iscontinuously performed without reducing the counter-electromotive power(the charging power of the battery) generated by the first rotatingelectrical machine, while the chargeable power of the battery is beingkept lower than a predetermined value, the chargeable power of thebattery may decrease early and thus the battery cannot accept thecounter-electromotive power, which makes it impossible to continue theinverter-less running control.

The present invention has been accomplished in view of theaforementioned problems, and it is therefore an object of the presentinvention to provide a hybrid vehicle capable of elongating a fail-saferunning distance under an inverter-less running control when thechargeable power of a battery has dropped lower than a predeterminedvalue.

The hybrid vehicle according to the present invention includes anengine, a first rotating electrical machine including a rotor providedwith a permanent magnet, an output shaft coupled to drive wheels, aplanetary gear device mechanically coupled to the engine, the firstrotating electrical machine and the output shaft, and configured totransmit torque among the engine, the first rotating electrical machineand the output shaft, a second rotating electrical machine coupled tothe output shaft, a battery, a converter configured to boost a voltagefrom the battery and output the boosted voltage, an inverter configuredto perform a power conversion between the converter and the firstrotating electrical machine and between the converter and the secondrotating electrical machine, and a controller configured to perform aninverter-less running control when at least one of the first rotatingelectrical machine and the second rotating electrical machine is notnormally driven by the inverter. The inverter-less running control issuch a control that the inverter is brought into a gate shut-off stateand the engine and the converter are controlled to cause the firstrotating electrical machine to generate a braking torque due to acounter-electromotive voltage generated by the first rotating electricalmachine, and thereby the vehicle is caused to run with a torque whichacts on the output shaft as a counterforce of the braking torque. Duringthe inverter-less running control, the controller is configured tocontrol a voltage difference between the counter-electromotive voltageof the first rotating electrical machine and the output voltage of theconverter to be a first voltage difference smaller than a second voltagedifference, the first voltage difference is the voltage difference whena chargeable power of the battery is lower than a predetermined value,and the second voltage difference is the voltage difference when thechargeable power of the battery is higher than the predetermined value.

According to the configuration mentioned above, during the inverter-lessrunning control, when the chargeable power of the battery has droppedlower than a predetermined value, the voltage difference between thecounter-electromotive voltage and the output voltage of the converter ofthe first rotary electrical machine is made smaller. Therefore, thecounter-electromotive power generated by the first rotary electricalmachine, namely the charging power of the battery is reduced.Accordingly, the charged amount of the battery is prevented from risingearly, and thereby preventing the chargeable power of the battery fromdecreasing early. As a result, it is possible to elongate the failsaferunning distance under the inverter-less running control when thechargeable power of the battery has dropped lower than a predeterminedvalue.

In some embodiments, the controller controls the voltage difference tobe the first voltage difference smaller than the second voltagedifference by increasing the output voltage of the converter.

According to the configuration mentioned above, even if the inverter isbrought into the gate shut-off state, it is possible to reduce thecharging power of the battery by controlling the converter.

In some embodiments, the controller controls the voltage difference tobe the first voltage difference smaller than the second voltagedifference by reducing a rotation speed of the engine.

According to the configuration mentioned above, thecounter-electromotive power of the first rotating electrical machine canbe reduced by decreasing the rotation speed of the engine. Since thevoltage difference between the counter-electromotive voltage and theoutput voltage of the converter of the first rotary electrical machineis decreased, it is possible to reduce the charging power of thebattery.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram schematically illustrating the overallconfiguration of a vehicle.

FIG. 2 is a circuit block diagram illustrating the configuration of anelectrical system and an ECU of the vehicle.

FIG. 3 is a diagram schematically illustrating an operation state of theelectrical system during inverter-less running.

FIG. 4 is a diagram schematically illustrating the relationship betweena MG1 rotation speed Nm1 and a counter-electromotive voltage Vc and therelationship between a MG1 rotation speed Nm1 and acounter-electromotive torque Tc.

FIG. 5 is a diagram illustrating an example of a control state duringthe inverter-less running in a nomographic chart.

FIG. 6 is a flowchart illustrating an example of a processing procedureperformed by the ECU. FIG. 7 is a diagram illustrating the relationshipbetween a chargeable power WIN for the battery and a system targetvoltage VHtag.

FIG. 8 is a flowchart illustrating another example of a processingprocedure performed by the ECU.

FIG. 9 is a diagram illustrating the relationship between a chargeablepower WIN for the battery and an engine target rotation speed Netag.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. It should be notedthat the same or equivalent portions in the drawings will be denoted bythe same reference signs, and the description thereof will not berepeated.

<Overall Configuration of Vehicle>

FIG. 1 is a block diagram schematically illustrating the overallconfiguration of a vehicle 1 according to the present embodiment.Vehicle 1 includes an engine 100, a motor generator (first rotaryelectrical machine) 10, a motor generator (second rotary electricalmachine) 20, a planetary gear mechanism 30, drive wheels 50, an outputshaft 60 coupled to drive wheels 50, a battery 150, a system main relay(SMR) 160, a power control unit (PCU) 200, and an electronic controlunit (ECU) 300.

Vehicle 1 is a hybrid vehicle that runs by using at least one of themotive power from engine 100 and the motive power from motor generator20. In normal running which will be described later, vehicle 1 canswitch the running mode between an electrical vehicle running mode inwhich the vehicle is driven to run by using the motive power from motorgenerator 20 without using the motive power from engine 100 (hereinafterreferred to as “EV running”) and a hybrid vehicle running mode in whichthe vehicle is driven to run by using both the motive power from engine100 and the motive power from motor generator 20 (hereinafter referredto as “HV running”).

Engine 100 is an internal combustion engine such as a gasoline engine ora diesel engine. Engine 100 is configured to generate the motive powerfor driving vehicle 1 to run in response to a control signal from ECU300. The motive power generated by engine 100 is output to planetarygear mechanism 30.

Engine 100 is provided with an engine rotation speed sensor 410. Enginerotation speed sensor 410 is configured to detect a rotation speed(engine rotation. speed) Ne of engine 100, and output a signalindicating the detection result to ECU 300.

Each of motor generators 10 and 20 is a three-phase AC permanent magnetsynchronous motor. At the time of initiating engine 100, motor generator10 can rotate a crankshaft 110 of engine 100 by using the electricalpower from battery 150. Motor generator 10 can also generate AC power byusing the motive power from engine 100. The AC power generated by motorgenerator 10 is converted into DC power by PCU 200 and charged intobattery 150. If necessary, the AC power generated by motor generator 10may be supplied to motor generator 20.

The rotor of motor generator 20 is coupled to output shaft 60. Motorgenerator 20 can rotate output shaft 60 by using the electrical powersupplied from at least one of battery 150 and motor generator 10. Motorgenerator 20 can also generate AC power through regenerative braking.The AC power generated by motor generator 20 is converted into DC powerby PCU 200 and charged into battery 150.

Motor generator 10 is provided with a resolver 421. Resolver 421 isconfigured to detect a rotation speed (MG1 rotation speed) Nm1 of motorgenerator 10, and output a signal indicating the detection result to ECU300. Similarly, motor generator 20 is provided with a resolver 422.Resolver 422 is configured to detect a rotation speed (MG2 rotationspeed) Nm2 of motor generator 20, and output a signal indicating thedetection result to ECU 300.

Planetary gear mechanism 30 is mechanically coupled to engine 100, motorgenerator 10 and output shaft 60, and is configured to transmit torqueamong engine 100, motor generator 10 and output shaft 60. Specifically,planetary gear mechanism 30 includes, as rotating elements, a sun gear Scoupled to the rotor of motor generator 10, a ring gear R coupled tooutput shaft 60, a carrier CA coupled to crankshaft 110 of engine 100,and a pinion gear .P meshing with sun gear S and ring gear R. Carrier CAis configured to hold pinion gear P in such a manner that pinion gear Pis capable of rotating and revolving.

Battery 150 is a rechargeable power storage device. Typically, battery150 is a secondary battery such as a nickel-hydrogen secondary batteryor a lithium ion secondary battery. SMR 160 is connected in seriesbetween battery 150 and PCU 200 via a power line. SMR 160 is configuredto switch between a conducted state in which battery 150 and PCU 200 areconducted to each other and a disconnected state in which battery 150and PCU 200 are disconnected from each other in response to a controlsignal from ECU 300.

PCU 200 boosts the voltage of the DC power supplied from battery 150,converts the DC power with a boosted voltage into AC power and suppliesthe AC power to motor generator 10 and motor generator 20. Further, PCU200 converts the AC power generated by motor generator 10 and motorgenerator 20 into DC power and supplies the DC power to battery 150. Theconfiguration of PCU 200 will be described in detail with reference toFIG. 2.

ECU 300 is provided with a central processing unit (CPU), a memory, aninput buffer and an output buffer or the like (none of them isillustrated in the drawings). ECU 300 controls various devices such thatvehicle 1 runs in a desired running state in accordance with a signalfrom each of the sensors and instruments as well as a map and a programstored in the memory. Note that the various controls are not limited tobe processed by software, and they may be processed by dedicatedhardware (such as an electronic circuitry).

<Configuration of Electrical System and ECU>

FIG. 2 is a circuit block diagram for illustrating the configuration ofan electrical system and ECU 300 of vehicle 1, PCU 200 includes acapacitor C1, a converter 210, a capacitor C2, inverters 221 and 222, avoltage sensor 230, and current sensors 241 and 242. ECU300 includes anHV-ECU 310, an MG-ECU 320, and an engine ECU 330.

Battery 150 is provided with a monitor unit 440. Monitor unit 440 isconfigured to detect a voltage (battery voltage) VB of battery 150, acurrent (battery current) IB flowing through battery 150, a temperature(battery temperature) TB of battery 150, and output a signal indicatingthe respective detection result to MG-ECU 320. Capacitor C1 isconfigured to smooth battery voltage VB and supply the smoothed voltageto converter 210.

Converter 210 is configured to boost battery voltage VB in response to acontrol signal from MG-ECU 320, and supply the boosted voltage to powerlines PL and NL. In addition, converter 210 is also configured to stepdown the voltage of the DC power supplied from one or both of inverters221 and 222 to power lines PL and NL in response to a control signalfrom MG-ECU 320 so as to charge battery 150.

More specifically, converter 210 includes a reactor L1, switchingelements Q1 and Q2, and diodes D1 and D2. Each of switching elements Q1and Q2 and switching elements Q3 to Q14 which will be describedhereinafter is for example an insulated gate bipolar transistor (IGBT).Switching elements Q1 and Q2 are connected in series between power linePL and power line NL. Diode D1 is connected between a collector and anemitter of switching element Q1 in inverse parallel to switching elementQ1, and diode D2 is connected between a collector and an emitter ofswitching element Q2 in inverse parallel to switching element Q2. Oneend of reactor L1 is connected to the high potential side of battery150, and the other end of reactor L1 is connected to an intermediatepoint between switching elements Q1 and Q2 (i.e., the joining pointbetween the emitter of switching element Q1 and the collector ofswitching element Q2).

Capacitor C2 is connected between power line PL and power line NL.Capacitor C2 is configured to smooth a DC voltage supplied fromconverter 210 and supply the smoothed voltage to inverters 221 and 222.

Voltage sensor 230 is configured to detect the voltage across capacitorC2, namely the output voltage VH (hereinafter referred to as “systemvoltage”) of converter 210, and output a signal indicating the detectionresult to MG-ECU 320.

As system voltage VH is supplied to inverter 221, inverter 221 convertsthe DC voltage into an AC voltage in response to a control signal fromMG-ECU 320 so as to drive motor generator 10. Thus, motor generator 10is driven to generate a torque specified by a torque command value TR1.

More specifically, inverter 221 includes a U-phase arm 1U, a V-phase arm1V and a W-phase arm 1W. The 3 phase arms are connected in parallel toeach other between power line PL and power line NL. U-phase arm 1Uincludes a switching element Q3 and a switching element Q4 which areconnected in series to each other. V-phase arm 1V includes a switchingelement Q5 and a switching element Q6 which are connected in series toeach other. W-phase arm 1W includes a switching element Q7 and aswitching element Q8 which are connected in series to each other. DiodeD3 is connected between a collector and an emitter of switching elementQ3 in inverse parallel to switching element Q3. In the same way, diodesD4 to D8 are each connected between the collector and the emitter ofeach of switching elements Q4 to Q8 in inverse parallel to thecorresponding switching element, respectively.

Inverter 222 includes phase arms 2U to 2W, switching elements Q9 to Q14,and diodes D9 to D14. Since the configuration of inverter 222 issubstantially equivalent to that of inverter 221, the descriptionthereof will not be repeated.

Current sensor 241 is configured to detect a current (motor current)MCRT1 flowing through motor generator 10, and output a signal indicatingthe detection result to MG-ECU 320. Current sensor 242 is configured todetect a current (motor current) MCRT2 flowing through motor generator20, and output a signal indicating the detection result to MG-ECU 320.

HV-ECU 310 is configured to generate an operation command forcontrolling motor generators 10 and 20, and output the operation commandto MG-ECU 320. The operation command for motor generators 10 and 20 mayinclude an operation permitting command and/or an operation prohibitingcommand (command for shutting off gates to inverters 221 and 222) forcontrolling each of motor generators 10 and 20, a torque command valueTR1 for controlling motor generator 10, a torque command value TR2 forcontrolling motor generator 20, a command value for controlling MG1rotation speed Nm1, a command value for controlling MG2 rotation speedNm2 and the like.

HV-ECU 310 is further configured to set a target output voltage(hereinafter referred to as “system target voltage”) VHtag for converter210, and output a signal indicating the value of the target outputvoltage to MG-ECU 320. HV-ECU 310 is further configured to determine anengine required power Pe*, and output a signal indicating the value ofthe engine required power to engine ECU 330.

MG-ECU 320 receives the operation command and system target voltageVHtag for motor generators 10 and 20 from HV-ECU 310. Furthermore,MG-ECU 320 receives signals from the respective sensors.

MG-ECU 320, based on the operation command and system target voltageVHtag as well as a variety of signals, controls converter 210 so as tomake system voltage VH equal to system target voltage VHtag. Morespecifically, MG-ECU 320, based on system target voltage VHtag, batteryvoltage VB and system voltage VH, generates a PWM-type (Pulse WidthModulation) control signal PWMC so as to cause each of switchingelements Q1 and Q2 to perform switching operations, and outputs thesignal to converter 210. On the other hand, MG-ECU 320, when receiving agate shut-off command of converter 210 from HV-ECU 310, generates a gateshut-off signal SDNC for shutting off respective switching elements Q1and Q2, and outputs the signal to converter 210.

In addition, MG-ECU 320 controls inverters 221 and 222 such that motorgenerators 10 and 20 operate in accordance with an operation commandreceived from HV-ECU 310. Since inverters 221 and 222 are controlled inthe same manner, the control on inverter 221 will be described only.When receiving an operation permission command for motor generator 10from HV-ECU 310, MG-ECU 320, based on system voltage VH, motor currentMCRT1 and torque command value TR1, generates a PWM-type control signalPWM1 so as to cause each of switching elements Q3 to Q8 to performswitching operations, and outputs the signal to inverter 221. On theother hand, MG-ECU 320, when receiving a gate shut-off command ofinverter 221 from HV-ECU 310, generates a gate shut-off signal SDN1 forshutting off respective switching elements Q3 to Q8, and outputs thesignal to inverter 221.

Furthermore, MG-ECU 320 detects malfunction in motor generators 10 and20. The malfunction information detected by MG-ECU 320 is output toHV-ECU 310. HV-ECU 310 is configured to be capable of reflecting themalfunction information to the operation command issued to respectivemotor generators 10 and 20.

Engine ECU 330 receives engine rotation speed Ne from engine rotationspeed sensor 410, and outputs the value to HV-ECU 330. Engine ECU 330controls the fuel injection, the ignition timing, the valve timing andthe like of engine 100 so as to make engine 100 operate under anoperating point (engine target rotation speed Netag and engine targettorque Tetag) determined based on engine required power Pe* determinedby HV-ECU 310.

In the example illustrated in FIG. 2, ECU 300 is divided into threeunits (HV-ECU 310, MG-ECU 320 and engine ECU 330), and however, ECU 300may be divided into four units or more.

Additionally, HV-ECU 310, MG-ECU 320 and engine ECU 330 may beintegrated into one unit. Hereinafter, HV-ECU 310, MG-ECU 320 and engineECU 330 will be described as ECU 300 representively.

ECU 300 calculates an SOC (State Of Charge) indicating a charged amountof battery 150. In general, the SOC is expressed by the ratio of anactual charged amount relative to the full charged capacity. The SOC maybe calculated by using various known methods such as a calculationmethod using the relationship between battery voltage VB and the SOC ora calculation method using the integrated value of battery current IB.Hereinafter, the SOC of battery 150 will be simply referred to as the“SOC”.

ECU 300, based on the SOC and battery temperature TB, sets a chargeablepower WIN (in watts) of battery 150. In the present embodiment, when theSOC is less than a predetermined value Si(for example, 60%), sincebattery 150 has enough rechargeable margin (the difference (in Ah)between the full charged capacity and the actual charged amount), ECU300 sets chargeable power WIN to a value greater than a predeterminedvalue W1. When the SOC exceeds predetermined value S1, ECU 300 limitchargeable power WIN to a value smaller than predetermined value W1 soas to prevent battery 150 from being overcharged, and ECU 300 setschargeable power WIN to a smaller value as the SOC increases. Inaddition, when battery temperature TB is not within a predeterminedrange, ECU 300 sets chargeable power WIN to a value smaller than thevalue set based on the SOC so as to prevent the deterioration of battery150.

Thus, ECU 300 controls engine 100 and motor generators 10 and 20 (PCU200) so as to prevent the power to be input to battery 150 fromexceeding chargeable power WIN.

<Normal Running and Inverter-less Running>

ECU 300 can control vehicle 1 to run under either normal mode orfail-safe mode.

The normal mode refers to such a mode that vehicle 1 is driven to runwhile switching as required between the EV running and the HV runningwhich are described in the above. In other words, the normal mode allowsthe electrical driving of motor generators 10 and 20 by respectiveinverters 221 and 222. Hereinafter, the running of vehicle 1 under thenormal mode is simply described as “normal running”.

The fail-safe mode refers to such a mode that when an malfunction hasoccurred and thereby the electrical driving of motor generators 10 and20 by respective inverters 221 and 222 cannot be performed normally(hereinafter the malfunction is referred to as “inverter malfunction”),vehicle 1 is driven to perform the fail-safe running by engine 100 whileshutting off the respective gates of inverters 221 and 222. In otherwords, the fail-safe mode does not allow the electrical driving of motorgenerators 10 and 20 by respective inverters 221 and 222. The invertermalfunction may include sensor malfunction in resolvers 421 and 422 andcurrent sensors 241 and 242 or the like, and communication malfunctionbetween MG-ECU and HV-ECU (hereinafter also referred to as “HV-MGcommunication malfunction”), for example. Hereinafter, the running inthe fail-safe mode will be described as “inverter-less running”, and thecontrol for performing the inverter-less running will be described as“inverter-less running control”,

FIG. 3 is a diagram schematically illustrating an operation state of theelectrical system during the inverter-less running. During theinverter-less running, in response to gate shut-off signal SDN1 from ECU300, all switching elements Q3 to Q8 included in inverter 221 are turnedinto the non-conductive state. Therefore, diodes D3 to D8 included ininverter 221 forms a three-phase full-wave rectifier circuit. Similarly,in response to gate-off signal SDN2 from ECU 300, all switching elementsQ9 to Q14 (see FIG. 2) included in inverter 222 are turned into thenon-conductive state. Therefore, diodes D9 to D14 included in inverter222 forms a three-phase full-wave rectifier circuit. On the other hand,switching elements Q1 and Q2 included in converter 210 continue toperform the switching operation in response to control signal PWMC fromECU 300.

Since engine 100 is driven during the inverter-less running, engine 100outputs engine torque Te, and motor generator 10 is dynamically(mechanically) rotated by this engine torque Te. Since motor generator10 is a synchronous motor, the rotor of motor generator 10 is providedwith permanent magnets 12. Thus, permanent magnets 12 provided in therotor of motor generator 10 are rotated by engine torque Te, and therebya counter-electromotive voltage Vc is generated. Whencounter-electromotive voltage Vc exceeds system voltage VH, a currentwill flow from motor generator 10 to battery 150, and thereby, acounter-electromotive torque Te will be generated in motor generator 10,acting to inhibit the rotation of motor generator 10.

FIG. 4 is a diagram schematically illustrating the relationship betweenMG1 rotation speed Nm1 and counter-electromotive voltage Vc and therelationship between MG1 rotation speed Nm1 and counter-electromotivetorque Tc. In FIG. 4, the horizontal axis represents MG1 rotation speedNm1, the vertical axis in the upper diagram representscounter-electromotive voltage Vc, and the vertical axis in the lowerdiagram represents counter-electromotive torque Tc.

In the rotation speed range illustrated in FIG. 4, counter-electromotivevoltage Vc increases in value as MG1 rotation speed Nm1 becomes higher.In a range where MG1 rotation speed Nm1 is lower than a predeterminedvalue Nvh, since counter-electromotive voltage Vc is less than systemvoltage VH, no current will be generated to flow from motor generator 10to battery 150. Therefore, no counter-electromotive torque Tc will begenerated.

In a range where MG1 rotation speed Nm1 exceeds predetermined value Nvh,since counter-electromotive voltage Vc is greater than system voltageVH, a current will be generated in response to the difference betweencounter-electromotive voltage Vc and system voltage VH (hereinafterreferred to as “voltage difference ΔV”), flowing in the direction frommotor generator 10 to battery 150. In other words, motor generator 10generates a counter-electromotive power, and battery 150 is charged bythe counter-electromotive power. In this occasion, counter-electromotivetorque Tc is produced according to the voltage difference ΔV in motorgenerator 10. Counter-electromotive torque Tc is a braking torque(negative torque) which acts to inhibit the rotation of motor generator10. The range where counter-electromotive torque Tc is generated (i.e.,where counter-electromotive voltage Vc exceeds system voltage VH) is aregion where the inverter-less running is allowed.

FIG. 5 is a diagram illustrating an example of a control state betweenengine 100 and motor generators 10 and 20 during the inverter-lessrunning in a nomographic chart of planetary gear mechanism 30. Inplanetary gear mechanism 30 configured as described with reference toFIG. 1, the rotation speed of sun gear S (which is equal to MG1 rotationspeed Nm1), the rotation speed of carrier CA (which is equal to enginespeed Ne) and the rotation speed of ring gear R (which is equal to MG2rotation speed Nm2) have a linear relationship in the nomographic chart(hereinafter also referred to as “nomographic relationship”).

During the inverter-less running, engine torque Tc is output from engine100. When motor generator 10 is mechanically rotated by engine torqueTe, it produces counter-electromotive voltage Vc. Ascounter-electromotive voltage Vc exceeds system voltage VH, motorgenerator 10 generates counter-electromotive torque Tc acting in adirection (negative direction) that inhibits the rotation of motorgenerator 10.

As counter-electromotive torque Tc is applied from motor generator 10 tosun gear S, a driving torque Tep is generated in ring gear R as areaction force of counter-electromotive torque Tc, acting in a positivedirection. Thus, Vehicle 1 is driven by driving torque Tep to performthe fail-safe running.

Meanwhile, motor generator 20 is also rotated by driving torque Tep, andthereby a counter-electromotive voltage will be generated in motorgenerator 20. However, as illustrated in the example of FIG. 5, sinceMG2 rotation speed Nm2 is lower than the rotation speed at which thecounter-electromotive voltage generated by motor generator 20 does notexceed system voltage VH, no counter-electromotive torque will begenerated in motor generator 20.

<Reduction of Battery Charging Power During Inverter-less RunningControl>

As vehicle 1 having the abovementioned configuration performs theinverter-less running, it is concerned that there may arise such aproblem that during the inverter-less running, battery 150 is charged byusing the counter-electromotive power generated by motor generator 10,and thereby the SOC will rise.

As described above, in a range where the SOC exceeds predetermined valueS1, chargeable power WIN is limited less than predetermined value W1,and chargeable power WIN is set to a smaller value as the SOC increases.As a result, while chargeable power WIN is being kept lower thanpredetermined value W1, if the inverter-less running control iscontinuously performed without reducing the counter-electromotive power(the charging power to battery 150) generated by motor generator 10,chargeable power WIN may decrease early, which makes it impossible tocontinue the inverter-less running control.

Thus, ECU 300 according to the present embodiment controls engine 100and converter 210 such that, when chargeable power WIN is smaller thanpredetermined value W1 during the inverter-less running control, thevoltage difference ΔV between counter-electromotive voltage Vc andsystem voltage VH becomes smaller than that when chargeable power WIN isgreater than predetermined value W1. Accordingly, thecounter-electromotive power generated by motor generator 10, namely thecharging power for battery 150 is reduced. Thereby, it is possible toprevent the SOC from rising early and prevent charging power WIN fromdecreasing early. As a result, even though chargeable power WIN dropslower than predetermined value W1, it is possible to continuouslyperform the inverter-less running control for a longer time, making itpossible to elongate the available fail-safe running distance under theinverter-less running control.

FIG. 6 is a flowchart illustrating a processing procedure performed byECU 300. This processing procedure is performed repeatedly at apredetermined cycle.

At step (hereinafter, the word “step” will be abbreviated as “S”) 10,ECU 300 determines whether the abovementioned inverter malfunction ispresent or not.

When the inverter malfunction is not present (NO at S10), ECU 300 setsthe control mode to the normal mode so as to perform the normal runningat S11.

When the inverter malfunction is present (YES at S10), ECU 300 sets thecontrol mode to the fail-safe mode so as to perform the inverter-lessrunning from S12 to S15.

Specifically, ECU 300 switches inverters 221 and 222 into the gateshut-off state at S12. Thereafter, at S13, ECU 300 calculates systemtarget voltage VHtag based on chargeable power WIN.

FIG. 7 is a diagram illustrating the relationship between chargeablepower WIN and system target voltage VHtag. As illustrated in FIG. 7, ina range where chargeable power WIN is larger than predetermined valueW1, system target voltage VHtag is set equal to predetermined voltageV1. On the other hand, in a range where chargeable power WIN is smallerthan predetermined value W1, system target voltage VHtag is set greaterthan predetermined voltage V1. More specifically, the smaller chargeablepower WIN is, the greater system target voltage VHtag will be set. Forexample, ECU 300 may store in advance the relationship illustrated inFIG. 7 as a map, and calculate system target voltage VHtag correspondingto the actual chargeable power WIN with reference to this map.

Returning back to FIG. 6, at S14, ECU 300 controls converter 210 so asto make system voltage VH equal to system target voltage VHtag which iscalculated at 513.

At S15, ECU 300 controls engine 100 so as to make engine speed Ne equalto engine target rotation speed Netag. In the present embodiment, enginetarget rotation speed Netag is adjusted according to MG2 rotation speedNm2 and the relationship in the nomographic chart so as to make MG1rotation speed Nm1 constant, and consequently, makingcounter-electromotive voltage Vc generated by motor generator 10constant (see FIG. 4).

Thereby, when chargeable power WIN for the battery drops lower thanpredetermined value W1, system voltage VH is increased (see FIG. 7)while keeping counter-electromotive voltage Vc constant. As a result,the voltage difference ΔV (=Vc−VH) between counter-electromotive voltageVc and system voltage VH becomes smaller, and the counter-electromotivepower generated by motor generator 10, namely the charging power forbattery 150 is reduced. Thereby, it is possible to prevent the SOC fromrising early and prevent charging power WIN from decreasing early.

As described in the above, ECU 300 according to the present embodimentdecreases the voltage difference ΔV between counter-electromotivevoltage Vc and system voltage VH by increasing system voltage VH whenchargeable power WIN drops lower than predetermined value W1 during theinverter-less running control. Accordingly, the counter-electromotivepower generated by motor generator 10, namely the charging power forbattery 150 is reduced. Therefore, it is possible to prevent the SOCfrom rising early and prevent charging power WIN from decreasing early.As a result, even though chargeable power WIN drops lower thanpredetermined value W1, it is possible to continuously perform theinverter-less running control for a longer time, making it possible toelongate the available fail-safe running distance under theinverter-less running control.

[Modification]

In the embodiment described above, the voltage difference ΔV is reducedby increasing system voltage VH. However, the voltage difference ΔV maybe reduced by using other methods. In the present modification, thevoltage difference ΔV is reduced by reducing engine rotation speed Ne.

FIG. 8 is a flowchart illustrating a processing procedure performed byECU 300 according to the present modification. The processing procedureis repeatedly performed at a predetermined cycle. It should be notedthat since the steps in FIG. 8 denoted with the same numbers as those inFIG. 6 have been described in the above, the detailed descriptionthereof will not be repeated.

When an inverter malfunction is present (YES at S10), ECU 300 switchesthe control mode to the fail-safe mode so as to perform theinverter-less running at S12 and from S16 to S18.

Specifically, ECU 300, after switching inverters 221 and 222 into thegate shut-off state at S12, calculates engine target rotation speedNetag based on chargeable power WIN at S16.

FIG. 9 is a diagram illustrating the relationship between chargeablepower WIN and engine target rotation speed Netag. As illustrated in FIG.9, in the range where chargeable power WIN is larger than predeterminedvalue W1, engine target rotation speed Netag is set equal topredetermined rotation speed N1. On the other hand, in the range wherechargeable power WIN is smaller than predetermined value W1, enginetarget rotation speed Netag is set smaller than predetermined rotationspeed N1. More specifically, the smaller chargeable power WIN is, thesmaller engine target rotation speed Netag will be set. For example, ECU300 may store in advance the relationship illustrated in FIG. 9 as amap, and calculate engine target rotation speed Netag corresponding tothe actual chargeable power WIN with reference to this map.

Returning back to FIG. 8, at S17, ECU 300 controls engine 100 so thatengine speed Ne becomes equal to engine target rotation speed Netagwhich is calculated at S16.

At S18, ECU 300 controls converter 210 so as to make system voltage VHequal to system target voltage VHtag. In the present modification,system target voltage VHtag is preliminarily set to a constant value, inother words, system voltage VH is constant.

Thus, when chargeable power WIN for the battery drops lower thanpredetermined value W1, while system voltage VH is being kept constant,engine rotation speed Ne is reduced and MG1 rotation speed Nm1 isreduced according to the relationship in the nomographic chart, andthereby, counter-electromotive voltage Vc generated by motor generator10 is reduced (see FIG. 4). Thus, it is possible to reduce the voltagedifference ΔV (=Vc−VH) between counter-electromotive voltage Vc andsystem voltage VH. As a result, similarly to the embodiment describedabove, when chargeable power WIN drops lower than predetermined valueW1, it is possible to continuously perform the inverter-less runningcontrol for a longer time.

The embodiment and the modification described in the above may becombined appropriately. That is to say, the voltage difference ΔV may bereduced by increasing system voltage VH and reducing engine rotationspeed Ne in combination appropriately.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the scopeof the present invention being interpreted by the terms of the appendedclaims.

What is claimed is:
 1. A hybrid vehicle comprising: an engine; a firstrotating electrical machine including a rotor provided with a permanentmagnet; an output shaft coupled to drive wheels; a planetary gear devicemechanically coupled to the engine, the first rotating electricalmachine and the output shaft, and configured to transmit torque amongthe engine, the first rotating electrical machine and the output shaft;a second rotating electrical machine coupled to the output shaft; abattery; a converter configured to boost a voltage from the battery andoutput the boosted voltage; an inverter configured to perform a powerconversion between the converter and the first rotating electricalmachine and between the converter and the second rotating electricalmachine; and a controller configured to perform an inverter-less runningcontrol when at least one of the first rotating electrical machine andthe second rotating electrical machine is not normally driven by theinverter, the inverter-less running control being such a control thatthe inverter is brought into a gate shut-off state, and the engine andthe converter are controlled to cause the first rotating electricalmachine to generate a braking torque due to a counter-electromotivevoltage generated by the first rotating electrical machine, and therebythe vehicle is caused to run with a torque which acts on the outputshaft as a counterforce of the braking torque, the controller beingconfigured to, when a SOC of the battery exceeds a value, set achargeable power of the battery to a smaller value as the SOC of thebattery increases so as to prevent the battery from being overcharged,during the inverter-less running control, the controller beingconfigured to: (i) when the chargeable power of the battery is higherthan a predetermined value, control a voltage difference between thecounter-electromotive voltage of the first rotating electrical machineand the output voltage of the converter to be a first voltagedifference; and (ii) when the chargeable power of the battery is lowerthan the predetermined value, control the voltage difference to be asecond voltage difference which is smaller than the first voltagedifference so as to prevent the chargeable power of the battery fromreducing early.
 2. The hybrid vehicle according to claim 1, wherein thecontroller controls the voltage difference to be the first voltagedifference smaller than the second voltage difference by increasing theoutput voltage of the converter.
 3. The hybrid vehicle according toclaim 1, wherein the controller controls the voltage difference to bethe first voltage difference smaller than the second voltage differenceby reducing a rotation speed of the engine.